US 3761936 A
A multi-beam array antenna assembly is disclosed, such assembly being adapted to form a plurality of simultaneously existing beams of radio frequency energy, each one of such beams having the gain of the entire antenna aperture and a different scan angle. The preferred embodiment of the contemplated assembly is fabricated, using printed circuit techniques and matching sections on a dielectric substrate, to form an array of antenna elements and constrained electrical paths for radio frequency energy between each one of the antenna elements and a number of feed ports. The electrical length of each one of such paths is adjusted so as to focus radio frequency energy in each one of the desired beams at a different feed port. The preferred embodiment also illustrates a multi-beam array antenna assembly having antenna elements spaced to increase the scan angle of each desired beam.
Claims available in
Description (OCR text may contain errors)
Tinned States Patent 1 1 1 ,761,936
Archer et a1. Sept. 25, 1973 1 MULTl-BEAM ARRAY ANTENNA Primary ExaminerEli Lieberman  Inventors: Donald Archer; Robert J. Attorney-Philip J. McFarland, Joseph D. Pannone and Prickett, both of Santa Barbara, Richard Sharkansky Calif; Curtis P. Hartwig, Lexington,
Mass.  ABSTRACT  Assignee: Raytheon Company, Lexington, A multi-beam array antenna assembly is disclosed, such Mass. assembly being adapted to form a plurality of simultaneously existing beams of radio frequency energy, each Flled' 7 May 1 1971 one of such beams having the gain of the entire antenna  Appl. No.: 142,149 aperture and a different scan angle. The preferred embodiment of the contemplated assembly is fabricated, using printed circuit techniques and matching sections  US. Cl. 343/754, 343/854, 333/84 M l b f f Im. CL q 14/06 on a 1e ectrlc su strate, to orm an array 0 antenna  Field li 755 771 elements and constralned electrical paths for radio fre quency energy between each one of the antenna elements and a number of feed ports. The electrical length of each one of such paths is adjusted so as to focus  References Cited radio frequency energy in each one of the desired UNITED STATES PATENTS beams at a different feed port. The preferred embodi- 3,52 ,l 2 8/1970 sakiotis et al. .t 343/854 ment also illustrates a multibeam array antenna assem- 3v623112 11/1971 PP etal 343/727 bly having antenna elements spaced to increase the 3,392,394 7/1968 Caballero v l 43/754 1 f h d d b 3,569,973 3/1971 Brumbaugh 343/771 Scan ang e O eac eslre earn 3 Claims, 2 Drawing Figures 76 o 570 -45b o 0 5d 0 57b 490 o Q o 579 i o M t A i 496, 476/ o o -.4 5c o 570 496 Q -45c/ o q 47e 0 577 57 v r49 0 '45? o i f O Q o t 57% 4 219 9 47 o 57g l 459 t 579 v r 57h o i 1 V 1 1 5 /7 a t 45/ 14 h o Q 57/ 49k 0 o 5J o 57/ 0 471 Q 45/ Patented Sept. 25, 1973 2 Sheets-Sheet :3
v v Hk v o R Ev kkv 9% Ev o fiw INVENTORS DONALD H ARCHER ROBERT J. PR/CKEW' CURT/S P HARTW/G MULTI-BEAM ARRAY ANTENNA BACKGROUND OF THE INVENTION This invention pertains generally to array atennnas for radio frequency energy and particularly to antennas adapted to form a plurality of simultaneously existing beams of such energy, the position in space of each one of such beams being independent, within broad limits, of the frequency of such energy.
It is known in the art that an array antenna may be arranged so that it produces a plurality of simultaneously existing beams of radio frequency energy. If such an array is properly designed, each one of the beams has the gain and bandwidth of the entire antenna aperture. According to the art, a desired number of simultaneous beams may be obtained by connecting each antenna element through a constrained electrical path to a plurality of feed ports, the constrained electrical path being made up of an electromagnetic lens which equalizes the time delay of the electromagnetic energy between any given one of a number of feed ports and all points on corresponding planar wave fronts of either transmitted or received energy.
Any one of a variety of known electromagnetic lenses may be used. For example, the individual antenna elements in an array may be connected through coaxial cables of varying lengths to radio frequency probes, the latter being inserted in a parallel-plane lens to which the feed ports are also coupled at points along the focal arc of the lens. While such an arrangement is satisfactory for many purposes, it has been found that, if air is the dielectric material in the parallel-plate lens, a relatively large lens is required. Consequently, a known multi-beam array may find little, if any, application where space is at a premium, as in airborne applications.
It is known in the art that the size of a parallel-plate lens may be decreased by using a dielectric material which has a dielectric constant greater than that of air. The use of such material has, however, in the past, been limited to applications in which a single beam is to be formed or the frequency of operation is to be limited within a relatively narrow band of frequencies because mismatches within the parallel-plate lens, or multiple reflections therein, combine to increase sidelobe levels and to distort the shape of the desired main beams. With conventional multi-beam array antenna systems, it has been customary to use orthogonal probes to couple radio frequency energy to and from a parallel plate lens. In order that such energy may be transferred efficiently, it has been found that such probes should be spaced away from conducting side walls of the lens at a distance of approximately one-quarter wavelength of the microwave energy (at the frequency of interest). Obviously, then, the bandwidth of the antenna system is limited by such a requirement because the optimum quarter-wave spacing of the orthogonal probes will vary with changes in frequency.
Another problem which is experienced with conventional multibeam array antenna systems is that discrete radio frequency components, such as transmission lines and directional couplers, must be used along with any known parallel-plate lens. It is evident, therefore, that extreme care must be taken in construction, assembly and use to ensure proper connection of the various elements making up such a multi-beam array antenna system. The magnitude of the problem may be appreciated when it is considered that literally thousands of radio frequency connectors are required in multi-beam array antennas of conventional design.
It is also characteristic of known multi-beam array antenna systems that the beam scan factor (meaning the ratio of the off-axis tilt of any radiated wave front and the angular location of each feed port from a reference line) is equal to 1. While such a characteristic is acceptable when a small number of beams is required or the off-axis tilt of any one beam is not great, say not over 30", it has been found that such a beam scan factor limits the usefulness of many arrays. That is, when a wide angle system is desired, it becomes almost impossible with known techniques to maintain beam shape at large scan angles.
SUMMARY OF THE INVENTION AND DESCRIPTION OF THE DRAWINGS Therefore, it is a primary object of this invention to provide an improved array antenna system for producing a number of simultaneously existing beams, such system incorporating a parallel-plate lens using a dielectric material having a dielectric constant greater than that of air.
It is another object of this invention to provide an improved array antenna system for producing a number of simultaneously existing beams, such antenna system being smaller in size than known antenna systems of such type.
Still another object of this invention is to provide, for use in an array antenna system of the type hereinbefore designated, a lens using a dielectric material having a dielectric constant greater than the dielectric constant of air, such lens utilizing printed circuit techniques to avoid internal mismatch and spurious reflections and to permit coupling of the resulting lens in a most efficient manner to the remaining portions of the antenna systern.
A further object of this invention is to provide an improved multi-beam array antenna system in which the number of required radio frequency connectors is reduced to a minimum.
A still further object of this invention is to provide an improved multi-beam array antenna system which is adapted to operate over a wide band of frequencies.
Another object of this invention is to provide an improved multi-beam array antenna system which may be used in applications requiring large beam scan angles.
These and other objects of this invention are attained generally by using printed circuit techniques to form a multi-beam array antenna assembly on a common substrate having a dielectric constant greater than that of air, such assembly including the required antenna elements, transmission lines and microwave lens to focus radio frequency energy at predetermined points along a focal arc of such lens, the transmission lines and microwave lens being printed in such a way on the common substrate as to form constrained paths for radio frequency energy, the assembly being completed by providing conventional coaxial connectors for coupling the microwave lens to external circuitry. For a more complete understanding of this invention, reference is now made to the following description of a preferred embodiment of this invention as illustrated in the accompanying drawing, in which:
FIG. 1 is a block diagram, greatly simplified, of a multi-beam array antenna assembly according to our inventive concepts incorporated in a direction finder, the illustrated antenna assembly being partially broken away to better show the details of its construction; and
FIG. 2 is a plan view of the substrate, the antenna elements and portions of the transmission lines and microwave lens of the multi-beam array antenna assembly shown in FIG. 1, such view illustrating how printed circuit techniques may be applied in the construction of multi-beam array antennas.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, it may be seen that the main sub-assemblies making up a direction finder incorporating the principles of this invention are a multi-beam array antenna assembly 10, a plurality (here 9) of receivers 11a through lli, a selector 13 and a utilization device 15. Except for the multi-beam array antenna 10, the just enumerated main sub-assemblies of the illustrated system are preferably conventional in construction. Thus, each one of the receivers 11a through lli may be a known heterodyne receiver adapted to convert radio frequency sisgnals to intermediate frequency signals derived from a different one of a similar plurality of feed ports (not numbered) of the multi-beam array antenna assembly 10. It is highly desirable that each one of the receivers 11a through lli be broadband, meaning responsive to any radio frequency signal within, say, a bandwidth in the order of an octave of frequencies. The selector 15, here illustrated in an extremely simple form for expository purposes, consists of an input selector switch 171' and an output selector switch 170, each having eight positions. Each one of such switches is operative sequentially to connect receivers 11b through lli to a detector 19. Receiver 11a is connected to a detector 21. The output terminals of the detectors 19, 21 are connected to a threshold circuit 23, as a differential amplifier, which in turn is connected, through a driver 25, to the output selector switch 170. To complete the circuit, each pole of the output selector switch 170 is connected, as shown, to a separate one of a plurality of indicator lamps 27b through 27i in the utilization device 15. It will be obvious, then, that the just-described selector l3 and utilization device 15 is effective, using the output signals from detector 21 as a reference signal, so as to cause different ones of the indicator lamps 27b through 27i to be lighted when signals above a predetermined level are present at the output terminal of corresponding ones of the receivers 11!) through 11h. It is equally obvious that the input selector switch 171' and the output selector switch 170 may be operated rapidly and cyclically so as to cause each one of the periodically actuated ones of the indicator lamps 27b through 27i to appear to be continuously lighted, thereby to provide a visual indication of the particular receivers 11b through lli which produce output signals. The particular ones of the receivers 11b through lli which produce output signals, in turn, indicate which ones of the beams formed by the multi-beam array antenna assembly 10 contain radio frequency energy, i.e. the direction of the origin of received radio frequency energy.
Obviously, the just-described apparatus is operative by reason of the inherent ability of an array antenna, as the multi-beam array antenna 10, to form simultaneously existing beams. Thus, in FIG. 1, the multi-beam array antenna assembly 10 is seen to consist, from the bottom up, of a laminar arrangement made up from a first metallic ground plate 31, a dielectric substrate 33 (on which circuitry 35 described in detail hereinafter is printed), a dielectric 37 and a second metallic ground plate 39 overlying the greater portion of the circuitry 35. It will be recognized that such an arrangement constitutes a conventional stripline configuration for providing constrained paths for radio frequency energy between input terminals (the antenna elements) and output terminals (the coaxial connectors to be mentioned). The laminar arrangement is fastened together in any convenient manner, say by a number of bolts, as those numbered 41. In passing, it will be noted that the number of bolts 41 is far in excess of the number required simply to hold the laminar arrangement together. The excess number of bolts 41, which number may vary as desired, serve to shield printed lines 47A through 47K and printed lines 578 through 57I of the circuitry 35 from one another.
It is essential to the invention that the material from which the dielectric substrate 33 be fabricated have a dielectric constant, or index of refraction, greater than that of air, here taken to be 1. For efficiency of operation and ease of fabrication, it is desirable that the dielectric substrate 33 have a relatively low loss tangent and that it be easily machined. For these reasons, it is here preferred that the dielectric substrate 33 be fabricated from a sheet of sintered magnesium titanate having a dielectric constant of approximately 16, although other materials may be used. For example, rutile (dielectric constant approximately or an epoxy base loaded with rutile (dielectric constant approximately 25) may also be used as the material for the dielectric substrate 33. It is preferred, although not essential, that the dielectric sheet 37 be fabricated from the same material as the dielectric substrate 33. At lower frequencies, say below S-band, the unbalance caused by using two different dielectric materials becomes insignificant. As a matter of fact the dielectric sheet 37 and the second metallic ground plate 39 may be omitted from the laminar assembly at such frequencies thereby converting the laminar arrangement to a conventional microstrip configuration. To complete the multi-beam array antenna assembly 10, a plurality (here 9) of conventional coaxial connectors 43a through 43h are disposed to provide nine output terminals for such assembly.
Referring now to FIG. 2, it may be seen that the circuitry 35 within the multi-beam array antenna assembly 10 here consists of particular printed circuits laid down on one surface of the dielectric substrate 33. Thus, an antenna element 45a is printed on the dielectric substrate 33 and connected, through a printed line 47a, to coaxial connector 43a (FIG. 1). It will be recognized that the directivity of antenna element 45a is that of a monopole (or an end fed conductor) antenna, i.e. approximately so that radio frequency signals from any source located within a 180 sector in the plane of the laminar arrangement are received by antenna element 45 and directed, via coaxial connector 43a, to receiver 11a (FIG. 1).
Antenna elements 45b through 45k, each of which is similar to antenna element 450, are connected through different lengths ofprinted lines 47b through 47k (each one of such lines including a matching section 49b through 49k) to a conductive surface of a parallel-plate lens 51. The intersections of such matching sections and the parallelplate lens 51 here describe an arc of a circle indicated by the dotted line marked 53. The second surface (sometimes referred to hereinafter as the focal are or the arc of best focus) of the parallel-plate lens 51 is indicated by the dotted line 55. Matching sections 57b through 57i are printed along the focal arc of the parallelplate lens 51, as shown. Each one of such sections, being faired into a different one of printed lines 57b through 571', constitutes a feed port (not num bered) for a different beam. Each one of such lines is, as shown in FIG. I, connected to a separate one of the coaxial connectors 43b through 43i. In passing, it will be noted that the number of antenna elements 45b 'thr'ough 45k may; and 'usually'will, differ from the number of feed ports. The number of the former and their disposition determine the shape and, to some extent, direction of the beams while the number and disposition of the latter determine the number of the beams and, along with the antenna elements 45b through 45k, the direction of the beams.
It will be recognized that, disregarding any mutual coupling between the various parts of the stripline configuration just described and any mismatches therein, the just-mentioned portions of circuitry 35, the dielectric substrates 33, 37 and the first and second metallic ground plates 31,39 constitute a two-dimensional constrained electromagnetic lens system having 5 of freedom. That is, there are five independent variables which may be changed in the design of the illustrated lens system: (I) the arrangement of the antenna elements 45b through 45k; (2) the length of each one of the printed lines 47b through 47k; (3) the shape of the parallel plate lens surface numbered 51 and the points of intersection of each one of the matching sections 49b through 49k therewith; (4) the shape of the parallel-plate lens surface numbered 53 and the points of intersection of each one of the matching sections 57b through 591' therewith; and (5) the dielectric constant of the material making up the dielectric substrate 33. It is known in the art, e.g. as shown in the paper entitled Wide Angle Microwave Lens for Line Source Applications by W. Rotman and R. F. Turner (Transactions of Antennas and Propagation, pp. 623-632, published in November, 1963, by the Institute of Electrical and Electronic Engineers, Inc., November, New York, N. Y.), that the first four parameters may be independently varied to produce a scanning array antenna. Thus, according to Rotman and Turner, the first four parameters may be selected to provide an array antenna assembly similar to that here shown, i.e. one in which the antenna elements lie on a straight line and the locus of the points of best focus lie on the arc of a circle having its center on the axis of symmetry of a parallel-plate lens. According to Rotman and Turner, when radio frequency energy is fed into the parallelplate lens from a feed port on the arc of best focus: (a) the electrical length of each path of such energy between any such feed port through the parallel-plate lens and the transmission lines to any antenna element and thence to a corresponding point on a planar wave front (which results from the diffraction pattern of the antenna elements) equals, to any desired degree (within, say, one-eighth ofa wavelength at the design frequency of the radio frequency energy) the electrical length of the path of such energy from such feed port through the centrally located antenna element to the same planar wave front; and (2) the scan angle (meaning the angular deviation from broadside) of the resulting beam of electromagnetic energy is the negative of the scan angle of the feed port (meaning the angular deviation of the feed port to which radio frequency energy is fed to the parallel-plate lens from the axis of symmetry of such lens). The shape of the beam is, as is well known, a function of illumination taper, and size of the antenna aperture, ie the number and spacing of antenna elements, and the frequency of the radio frequency energy. A moments thought will make it clear that the design criteria of the scanning array antenna just described may serve as the basis for the design ofa multibeam array antenna for transmitting radio frequency energy. Thus, if instead of using a single feed port along the arc of best focus, a number of such ports are fed simultaneously with radio frequency energy, a corresponding number of beams, each with a different scan angle, will be formed. It is obvious that such an antenna may be used to receive radio frequency energy as illustrated.
The just-mentioned design approach is adequate when the scan angle of any beam of electromagnetic energy is less than, say 35. For greater scan angles, the path length errors caused by unavoidable differences in the lengths of the various electrical paths within the parallel-path lens render the conventional Rotman/- Turner approach infeasible. We have found, however, that a decrease in the spacing between the antenna elements 45b through 45k from the spacing required by straightforward application of the Rotman/Turner formulas is an effective way to increase the scan angle of the radiated beam. Thus, after calculating the dimensions of a desired array antenna assembly, the spacing between adjacent elements may be decreased so that the following equation is true:
S /S sin b/sin a where S is the spacing, in wavelengths,
of the antenna elements as calculated according to the Rotman/Turner approach;
a is the angular deviation of any feed port from the axis of symmetry of an array antenna;
1; is the desired scan angle of the beam from the array antenna; and
S is the spacing, in wavelengths, between antenna elements required to obtain the desired scan angle b.
Thus, by decreasing the spacing between antenna elements, the scan angle may be increased to a maximum of for a linear array of antenna elements without increasing the effect of path length errors in the array antenna assembly. It will be noted, in passing, that the decrease in spacing, additionally, increases the frequency of operation at which grating lobes are formed by the illustrated array antenna assembly. Referring to FIG. 2 to illustrate the foregoing, let it be assumed that, in accordance with the Rotman/Turner approach, the spacing, SRT, for a scan angle of 30 would be equal to the spacing between every other antenna element. Then, in accordance with our concept, it may be easily calculated that sin b equals 1 in the illustrated case. In other words, the scan angle, b, of the beam in the illustrated array corresponding to the beam having a scan angle of 30 in a Rotman/Turner array would be 90. Obviously, the ratio between SRT and S could be selected as desired to increase scan angle by any desired amount.
The physical size of known array antenna assemblies made with a parallel-plate lens and coaxial transmission lines is relatively great. That is, because the velocity of propagation of electromagnetic energy in either coaxial transmission lines or a parallel-plate lens with air as a dielectric approaches the velocity of propagation of electromangetic energy in free space, the use of elements (especially when it is desired to focus and/or collimate radio frequency energy passing from or to an antenna with a large aperture) results in a lens system having a relatively long focal length. It follows, then, that the arc of best focus must be physically spaced a correspondingly large distance from the antenna aperture. In applications in which physical size is at a pre-' mium, such a requirement of known parallel-plate lenses militates against their use in array antennas. We have, however, by incorporating dielectric material having a dielectric constant greater than the dielectric constant of air in a multi-beam array antenna assembly, effected a reduction in the velocity of propagation of radio frequency energy therein, with a concomitant reduction in the physical size of such an assembly. Thus, we have found that if an array antenna assembly is designed following the teachings of Rotman and Turner, the physical dimensions of the parallel-plate lens and the length of the required transmission lines may be scaled down from the dimensions required with air as the dielectric material by a factor equal to the square root of the dielectric constant of the dielectric material used as a substrate.
In a practical array antenna assembly using a parallelplate lens and transmission lines it is not possible to overlook the effects of mutual coupling and mismatches. That is, the VSWR for electromagnetic energy within such an assembly must be carefully controlled in order to avoid excessive insertion losses and internal reflections. Thus, in known array antenna assemblies it is common practice to provide matched coupling between the parallel-plate lens and the transmission lines, as by conventional impedance transformers. Unfortunately, as the frequency of the radio frequency energy changes from a nominal design frequency, the use of matching sections such as impedance transformers (which are frequency-sensitive) changes an inherently broadband antenna arrangement to a relatively narrow band one.
Even if the parallel-plate lens and transmission lines of known array antennas are perfectly matched at a design frequency, the problem of coupling discrete and separate elements with respect to each other to permit efficient power transfer remains. Thus, in order that radio frequency energy be transferred efficiently between a parallel-plate lens and a number of transmission lines by means of orthogonal coupling devices, the positioning of such devices is critical, being optimum only at the design frequency. Consequently, when the frequency of the radio frequency energy is changed from a design frequency, the efficiency of power transfer decreases. Again, an inherently broadband arrangement is converted into a relatively narrow band arrangement.
The foregoing difficulties are obviated to a large degree by following our concept of replacing the discrete and separate elements ofa radio frequency lens sytem, i.e. the coaxial transmission lines and parallel-plate lens heretofore used in array antenna assemblies, with stripline or microstrip circuits integrally formed on a dielectric substrate along with the desired antenna elements. As a consequence, the parallel-plate lens, the transmission lines and the antenna elements may be printed, as illustrated in FIG. 2, on one side of a dielectric substrate in such a manner as to permit matching sections to be formed integrally therewith. Consequently, no frequency-sensitive circuit elements, as orthogonal probes, are inserted in the path of radio frequency energy within the multi-beam array antenna assembly 10 (FIG. 1). Further, because of the ease with which the shape of the printed matching sections may be changed, it is possible to adjust the shape of each section for optimum performance. Therefore, by following our concepts in the design 'of a multi-beam array antenna for any particular application, the bandwidth of the resulting assembly will be limited only by the disposition of the antenna elements with respect to each other.
It will be recognized that the dielectric constant of known solid dielectric materials varies with changes in temperature. Such a characteristic change obviously changes the electrical length of the various constrained paths for radio frequency energy within the described array antenna assembly. In the ordinary case the electrical length of each one of the various constrained paths varies proportionally with the original length thereof. It follows, then, that the electrical lengths of the various paths vary relatively with respect to each other with changes in temperature. Such relative changes, in turn, disturb the phase relationships between the various portions of the radio frequency energy in passing through the assembly so as to cause, for any beam other than the broadside beam, a shift in beam direction. The amount of such shift increases with scan angle. It is evident, however, that conventional temperature control techniques, placing the array antenna assembly in a thermostatically controlled heating unit, may be used whenever necessary or desirable to avoid any deleterious effects of changes in ambient temperature.
It will also be evident that many other changes and modifications may be made in our preferred embodiment without departing from our inventive concepts. For example, the spacing between the antenna elements and the disposition thereof may be varied as desired to change the shape or direction of beams. Similarly, the number and disposition of the feed ports may be varied to change the direction and number of beams. Additionally, the transmission lines between the antenna elements and the parallel-plate lens may be broken to allow insertion of radio frequency amplifiers in each one of such lines. Further, the surface of the dielectric substrate, and, if used, the surface of the dielectric sheet nearer to the printed circuits need not be planar. That is, such surfaces may be indented between the printed circuits in any convenient way to improve isolation between the different portions of such cir cuits. Finally, linear multi-beam array antennas of the type disclosed may be arranged to form a planar array or may be used instead of a single beam array which is scanned either electrically or mechanically. It is felt, therefore, that this invention should not be restricted to its disclosed embodiment but rather should be limited only by the spirit and scope of the appended claims.
What is claimed is:
1. In an antenna array assembly wherein any one, or ones, of a first plurality of feedports disposed along an arcuate path may be actuated with microwave energy to energize a second plurality of antenna elements disposed to form a linear array, the direction of the beam, or beams, of microwave energy propagated by such array being dependent upon the one, or ones, of the actuated feedports, an improved microwave lens and transmission line arrangement interconnecting the first plurality of feedports with the second plurality of antenna elements, such arrangement comprising a section of stripline including:
a. a printed circuit conductor having an irregular geometrical shape to define a different constrained electrical path between each one of the first plurality of feedports and each one of the second plurality of antenna elements; and,
b. a dielectric spacer overlying the center conductor, the dielectric constant of such spacer being greater than unity.
2. The improved microwave lens and transmission line arrangement as in claim 1 wherein the center conductor of the stripline includes:
a. a printed portion having a first and a second curved side, the feed ports being coupled to points along the first curved side; and
b. a first plurality of printed lines, one end of each different one thereof being coupled to a different one of the first plurality of antenna elements and the second end of each different one of such lines being coupled to points along the second curved side of the printed portion.
3. The improved microwave lens as in claim 1 wherein the electrical length of each different constrained electrical path between any one of the feedports and successive ones of the antenna elements differs progressively by an amount equal to the difference in the electrical length between any successive pair of antenna elements and a planar wavefront of microwave energy.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Inventor(s) Donald H. Archer, Robert J. Prickett and Curtis Hartwig It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
In the Specification Column 1, line 28, "paral1el plane should be -parallelplate-- Column 3, line 23, "sisgnals" should be -signals Column 3, line 40, "170" should be -.l7o-
Column 4, line 4, after 'dielectri'c" add -sheet-- Column 5, line 27, change to --degrees-- Column 5, line 43, change "of" to --on- In the Claims Column 9, line 11 after "circuit" add -center-- Signed and Scaled this twenty-eight D ay Of October 1975 [SEAL] Arrest:
RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ofParents and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION patent 3 ,761,936 Dated eptember 25 1973 Inventor(s) Donald H. Archer, Robert J. Prickett and Curtis Hartwig It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
In the Specification Column 1, line 28, "parallel\plane should be -parallelplate-- Column 3, line 23, "sisgnals" should be -signals- Column 3, line 40, "170" should be l'7o- Column 4, line 4, after "dielectric" add sheet-- Column 5, line 27, change to -degrees-- Column 5, line 43, change "of" to -on In the Claims Column 9, line 11 after "circuit" add center-- Signed and Sealed this twenty-eight D ay Of October 1 975 [SEAL] Attest:
RUTH C. MASON C. MARSHALL DANN Arresting Office'r Commissioner uj'Parents and Trademarks